VIBRATIONAL-MODES OF LIQUID N-ALKANES - SIMULATED ISOTROPIC RAMAN-SPECTRA AND BAND PROGRESSIONS FOR C5H12-C20H42 AND C16D34

The isotropic Raman spectra of the liquid n-alkanes C5H12 through C20H42 along with C16D34 were calculated using a simple intensity model. The calculated spectra closely resemble the observed spectra. Well-defined patterns in the spectra are revealed when the frequencies of the Raman bands are assembled together for the liquids C-5-C-20. The patterns observed are associated with the existence of band progressions. These resemble the progressions found in the spectra of the all-trans chains in the crystal. The introduction of conformational disorder into an assembly of ordered chains affects the frequencies of the bands much less than the distribution of intensity. A rationale for this behavior is presented. The vibrational modes of C16H34 and C16D34 have been characterized, both for the crystal and for the liquid, in terms of the frequency distribution of the potential energy for specific kinds of vibrational modes.